Research On The Soldering Ability And Reliability Of Sn2.5Ag0.7Cu0.1RExNi/Cu Solder Joints

The orientation of electronic packaging tends to high density, high accuracy, finepitch and micro-dimension with the rapid development of electronic informationindustry made the soldering ability and reliability more and more important.Developing environment-friendly and high reliable lead-free solder which can replaceSnPb solder is one of the hot spots in micro-electronic connection materials field.SnAgCu system solder alloy such as SnAgCuRE lead-free solder, which is consideredas one of the most potential succedaneums of SnPb solder, is expected to beextensively used in the future. However, the strength and reliability of this lead-freesolder alloys is still insufficient, and can’t satisfy the requirement of higher quality forthe solder joint in the micro-jointing field, developing lead-free solder alloys with highstrength and reliability has vital effect on improving the quality of electronicproduction.In the paper, adopting the orthogonal test, the effect of Ni content, flux, solderingtemperature and time on the microstructure of interfacial intermetallic compound（IMC） and property of Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints are researched mainly,and the optimum soldering parameter can be obtained. On this basis, the effect of Niand other aging parameters on the microstructure, growth kinetic of interfacial IMCand fracture mechanism of the solder joints are researched, and the optimumcomposition of the Sn2.5Ag0.7Cu0.1RExNi lead-free solder alloys is finallyconfirmed.The results reveal that adding proper quantities Ni in Sn2.5Ag0.7Cu0.1RE solderalloys can refine the initial β-Sn phase and eutectic structure, suppress the growth ofthe（Cu,Ni）₆Sn₅at the interface of solder joints, and reduce the roughness of interfacialIMC, improve the shear strength of the Sn2.5Ag0.7Cu0.1RExNi/Cu solder joints. Thesolder alloy structure was fine and homogenous, eutectic structure proportion waslarge, interfacial IMC was thin and flat, the grain size of （Cu,Ni）₆Sn₅was small, the shear strength got the maximum value （45.6MPa） when the Ni content was0.1%,which was15.2%higher than the solder joints without Ni added.With the aging time increasing, the thickness of （Cu,Ni）₆Sn₅and Cu3Sn increases,the morphology of （Cu,Ni）₆Sn₅changes from rough scallop-tape to smooth planar-tapeand its top-view morphology changes from small-sized cobblestone-tape to large-sizedpolyhedron-tape. Adding proper quantities Ni in solder alloys can reduce theroughness and edges number of IMC, increase the growing activation energy of IMCand suppress the growth of IMC, inhibit the fracture changing from ductile type tobrittle type, which retard the reduction of solder joints shear strength during aging. The（Cu,Ni）₆Sn₅and Cu3Sn have the largest activation energy which is86.8kJ/mol and93.7kJ/mol, respectively; and the shear strength of the solder joint is the highest with0.1%Ni addition.Taking the soldering ability and reliability into consideration, Sn2.5Ag0.7Cu0.1RE0.1Ni lead-free solder alloys have the eximious combination properties, which canmeet with the need of high strength and reliability solder joints in the contemporarymirco-jointing field.